Are Premium Forum Platforms Worth Paying For?

[Serene]

With Discourse, XenForo, Flarum, phpBB, vBulletin and others around, premium software often claims faster growth and better user experience. But is the investment justified for small or mid-sized communities? Or can free open-source platforms deliver similar performance with good management and smart plugins? What are your experiences with upgrades and ROI of paid licenses?